Luminescent bacteria emit light as a result of a series of redox reactions, the last of which is catalyzed by the enzyme luciferase. The energy for the emission process is derived from the electron transport chain at the NADH level and transferred to FMNH2. While light emission is the most obvious product of the reaction, heat is also evolved. Recent work has demonstrated that the total amount of heat evolved is in excess of 80 kcal (mol FMN)-1. The energetics of the reaction indicate a discrepancy between the observed quantum yield and the ratio of h nu/delta G. The reaction also appears to generate a long-term heat effect which has been interpreted in terms of a long-lived species. We are also involved in thermal titrations of the enzyme with a variety of ligands under a variety of conditions. The proposed study is designed to provide a detailed thermodynamic description of the chemical and physical events leading to photon emission. BIBLIOGRAPHIC REFERENCES: McIlvaine, P. M. and Langerman, N. "A Calorimetric Investigation of the Growth of the Marine Luminescent Bacteria Beneckea harveyi and Photobacterium leiognathi (1977) Biophys. J. 17 17-25. Beaudette, N. V., Langerman, N., Kisliuk, R. L. and Gaumont, Y. L. "A Calorimetric Study of the Binding of 3'-deoxyuridine-5'-phosphate and 5-fluoro-3'-deoxyuridine-5' -phosphate to Thymidylate Synthetase" (1977) Arch. Biochem. Biophys. 179 272-278.